Pros and Cons of feathering props

[Gamechanger]

I recently bought a Variprop feathering prop for my Irwin 43 MKIII sloop. I going from a fixed prop so my purpose for making the change include increasing speed when under sail (without engine on) and reducing the prop walk I currently have when in reverse gear. My hope is to gain about 1 knot of speed and virtually eliminate prop walk. Am I fooling myself??

[robert sailor]

You might be. If the winds are strong enough the extra drag of a fixed prop can be overcome by the extra drive of the wind but anything below that point you will pick up additional speed and in light air in can be as much as a knot. Prop walk can vary depending on the design of the prop.

[Jim Cate]

The amount of improvement in boat speed will depend largely upon what sort of fixed prop you had originally! If it was a large area three blade, the one knot figure might well be achleved. If it was a skinny "sailboat" two blader, not so much.

In general, the speed region where the improvement will be greatest is in the mid ranges, not in very light air. Under very light conditions, skin friction from the hull is the largest contributor to drag, and as you approach hull speed, wave making becomes the culprit. It is the in-between speeds where prop drag is most important.

But for sure, you should enjoy improved performance with the new one! Exactly how much... hard to say accurately!

Jim

[sailorboy1]

I have a flexofd feathering prop. It still has some prop walk when I spin the prop slow and I like that as sometimes having it is a nice thing.

But I got it for the sail speed, and the quiet of the shaft not spinning while sailing!!!

[sandy stone]

I think a Flex-o-fold is a folding prop (I had one on a previous boat). I now have a Maxprop, which is feathering. It's great for sailing, has a ton of thrust in reverse, probably the best feature, but I still have significant prop walk. I don't think there's any getting rid of that, you just have to learn to use it to your advantage.

[sailorboy1]

Yes the fof is a folding. I had a maxprop on last boat. I don't care what they say, it didn't have less prop walk and it also was less efficient in forward and that boat was smaller but burned more fuel

[meirriba]

I do not think that propwalk is connected to feathering. It is caused by the asymmetry of revolution. If you want to get rid of the walk - install two props (of any kind) that revolve (and are designed to) in counter direction.

[david knowles]

on average you'll get Half a knot, but every little bit helps. You still will have prop walk

[S/V Alchemy]

I went from a three-blade fixed 18 x 13 to a four-bladed 19 x 15 (nominal) Vari-Prop.

At the same time I went from a 52 HP to a Beta 60 on a steel full-keeler.

I would say that whilst you have to be prepared for the slight lag time as the prop feathers from forward to reverse, that you will "dock with more authority" and will get more speed under sail; the loading and wetted surface will determine how much.

I am very pleased with the new motor and prop. I can maneuver far more effectively in tight spots now than I could with the fixed prop. Experiment with an empty sea wall and all fender out until you get the "feel" down.

[a64pilot]

I put an autoprop on my IP. I expected to gain some in light winds, cause everyone says you will. Now an IP is no light wind performer or race boat by any means
I didn't get squat in light winds, but as Jim said I get a lot in higher wind speeds and if you think about it for a second it makes sense, prop drag at 3 kts is very little so even if you eliminated it, its not going to make much difference, but at 7 kts its a lot, and there the difference shows.

However almost every feathering prop has no blade shape, they are flat plates, and therefore inefficient when motoring, the shape on a fixed prop is there for a reason, it works. So be aware of that.
Also I believe the prop walk is a function of pitch more than anything, a high prop pitch will gives lots of walk, and a flatter pitch won't. My autoprop has almost zero prop walk, but at very low speeds, its pitched very flat too. So if you can set your reverse pitch and set it flatter you will I believe reduce prop walk and likely reverse thrust too

[undercutter]

We also have a sari prop and we did not notice a distinct improvement under sail however the prop walk is much better.

Make sure that you grease regularly and remove from the shaft at a minimum every 2 years. Did you buy the puller with the prop?

[degouwb]

I bought my Passage 42 used, with a three blade Variprop.
After 5 years of sailing and docking with this prop , I decided to have the original fixed prop checked and balanced and installed.
Even though the Variprop was checked for proper pitch I was never convinced that it was better than the original.
There was only one way to find out and that was to make the change.
Is there any prop walk? You bet, but than you learn to use that to your advantage as time goes by.
I'm no racer and single hand most of the time.
I find the fixed prop makes my boat handling more predictable.
I'm sure the scientists in the group will show you my foolishness, but I'm happy.

[Martkimwat]

My boat originally had a three blade fixed, when I went to a two blade folder I immediately noticed around 3/4 knot improvement in medium airs F3~F5 but the bummer was virtually no stopping power, a function of much less efficiency in reverse due to it not opening fully and the idiosyncracy of Yanmar diesel gearboxes which have a single very low ratio astern gear (3:1) regardless of forward ratio, in my case 2.1:1. I ended up a year later changing to a 3 blade Featherstream feathering prop. I didn't see any reduction in sailing speed from the folder but a very slight drop in forward speed under power ( Featherstream claim less than 5% drop in efficiency) I also gained vastly improved stopping power, even over the fixed prop. That's really important, as I'm on pile moorings at right angles to the prevailing wind and I usually have go into the mooring from downwind, it being shared with another boat and I sometimes have as little as 5 feet between my mooring and the shore at low tide which exacerbates things as I have to have the keel raised too. I am also singlehanded most of the time. I need to be able to stop smartly and pick up my lines before the wind blows me off. same goes for coming alongside jetties or pontoons if the wind is blowing me off. My boat doesn't seem to be to badly affected by propwalk and I didn't notice any difference between the props in that regard but in conclusion I think you will find a marked sailing improvement over a fixed three blade if that is what you have at present.

[buzzstar]

Interesting thread. I have never used a feathering prop because of a concern, probably unwarranted, that due to an unspecified mechanical problem (not thought through, but, vaguely in my mind, perhaps corrosion, sea life or a breakage?) I would suddenly find I had no prop. I've never discussed or considered the matter enough even to bother with looking into it. This did not change my mind about not having one, but based on my needs it provided a rational reason. I really do not worry so much about the speed, although even one knot or a half knot can be important at times. I've learned to live with what I have in reverse, and it may or may not matter in that aspect anyway.

[Mutt]

Veriprop recomended 12 in of pitch for my 3 blade prop (16x12). I had lots of prop walk and I was doing 6 knots at 1600 rpm. I reduced the pitch to 10 inches and prop walk is much less and now 6 knots at 2000 rpm which is much more reasonable for my boat. The moral of the story is that the recommendations from Variprop are not always correct, are an easy adjustment.